1. Field of the Invention
The present invention relates to a method for treating or inhibiting the development of a disease, disorder or condition, which is associated with increased capillary permeability and white blood cell extravasation, such as brain inflammation and sepsis.
2. Description of the Related Art
Arachidonic acid (AA) is released from phospholipid in the cell membrane to the cytoplasm in response to a number of insults such as mechanical, thermal, chemical, bacterial and other insults, and its products (the eicosanoid compounds prostaglandins and leukotrienes) have been found to be biologically important in a number of ways. Most of the eiconosaid compounds tend to aggravate inflammatory, pain, and fever responses, and they have been the targets of extensive research on anti-inflammatory and analgesic drugs. For example, anti-inflammatory steroids such as cortisone function by suppressing the phospholipase enzymes that generate arachidonic acid from membrane phospholipids. Pain-killers such as aspirin and ibuprofen act by blocking to some extent the cyclooxygenase enzymes that control the conversion of arachidonic acid to the eicosanoids, prostaglandins, prostacyclins, and thromboxanes.
Additionally, it is known that prostaglandins and leukotrienes contribute to the genesis of inflammation in both the peripheral and central nervous system (CNS). Despite studies done over three decades, exactly how prostaglandins contribute to inflammation remains unclear. In contrast, recent studies using leukotriene receptor antagonists indicate that leukotrienes might play a major role in this process.
Leukotrienes are potent lipid mediators and are divided into two classes, based on the presence or absence of a cysteinyl group. Leukotriene B4 does not contain such a group, whereas leukotriene C4, D4, E4 and F4 are cysteinyl leukotrienes. These compounds have been recognized as inflammatory agents since the early 1980's (von Sprecher et al., 1993 and Piper, 1984).
In the 1990's, various drugs known as “leukotriene antagonists”, which can suppress and inhibit the activity of leukotrienes in the body, were identified. The term “leukotriene antagonist” is used herein in the conventional medical sense, to refer to a drug that suppresses, blocks, or otherwise reduces or opposes the concentration, activity, or effect of one or more subtypes of naturally occurring leukotrienes. However, such leukotriene antagonists can be classified into two different groups based on a difference in mechanism of action, one which to suppresses 5-lipoxygenase and the other which competitively antagonizes the receptor for leukotriene. Pranlukast, which is one leukotriene antagonist, acts strictly at the leukotriene C4 and D4 receptor level.
Although some leukotriene receptor antagonists have been disclosed for use in treating brain inflammation (e.g., J63258-879-A, J02-169583-A, WO9959964-A1, EP-287-471-A), all of the disclosed leukotriene receptor antagonists are presumed to pass the blood-brain barrier (BBB) because it is conventional wisdom that a molecule must be able to pass the blood-brain barrier in order to reduce or inhibit brain inflammation, or to treat disorders of the brain resulting from brain inflammation (Wilkinson et al., 2001). As leukotriene C4 and D4 receptor antagonists do not pass the blood-brain barrier, insofar as is known, the leukotriene C4 and D4 receptor antagonists have never previously been used to treat or prevent brain inflammation except for a neuroprotective effect of pranlukast (ONO-1078), a leukotriene receptor antagonist, on focal cerebral ischemia in rats (Zhang et al., 2002) and in mice (Zeng et al., 2001). The leukotriene C4 and D4 receptor antagonists are, however, commonly used to treat asthma. The leukotriene C4 and D4 receptor antagonist pranlukast is used clinically as an anti-asthmatic drug and is known to have few side effects. Pranlukast does not pass, or passes the blood-brain barrier at most at a very minimal level, akin to the other antagonists such as zafirlukast and montelukast. Other off-label uses have been suggested for these compounds, including treatment of allergic diseases (Shih, U.S. Pat. No. 6,221,880) and for use in treating migraine and cluster headaches (Sheftell et al., U.S. Pat. No. 6,194,432).
Generally, capillaries are lined with endothelial cells that have various openings, such as intracellular clefts, fenestrae and pinocytotic vesicles. Unlike these general capillaries, brain capillaries are characterized by the relative absence of these openings between endothelial cells, but instead have tight junctions originated from the periphery. Furthermore, central capillaries are surrounded by astroglia cells, which are disposed over these tight junctions of endothelial cells (originating from the periphery). The blood-brain barrier (BBB) is a capillary barrier comprising a continuous layer of tightly bound endothelial cells. These cells permit a low degree of transendothelial transport, and exclude molecules in the blood from entering the brain on the basis of molecular weight and lipid solubility, as described in Neuwelt (1980). For example, the blood-brain barrier normally excludes molecules with a molecular weight greater than 180 daltons. In addition, the lipid solubility of molecules is a major controlling factor in passage through the blood-brain barrier.
The function of the blood-brain barrier is to maintain the homeostasis of the neuronal environment. Small molecules (M.W.<200 daltons) having a high degree of lipid solubility and low ionization at physiological pH freely pass through the blood-brain barrier. In addition, the blood-brain barrier allows water to move in either direction in order to maintain equal osmotic concentrations of solutes in the extracellular cerebral fluid.
The unique biological aspect of the blood-brain barrier is an important focus in treating central nervous system (CNS) disorders. While the interendothelial junctions between the cells of the blood-brain barrier are normally designed to keep potentially noxious substances away from the brain, this condition changes during inflammation. In other words, the permeability of the blood brain barrier increases. Brain inflammation, e.g., due to stroke or physical head injury, is a serious medical problem causing much human misery.
The therapeutic challenges posed by brain inflammation have been tackled using the following approaches: (1) Osmotherapy, i.e., reducing the intracranial pressure by osmotic withdrawal of water from the brain tissue by intravenously administering such substances as mannitol, glycerol, urea to increase the osmolality of the blood brain barrier. Disadvantages include side effects such as electrolyte disturbances and renal failure. (2) Steroid therapy that reduces the local capillary leakage and global metabolic depression by means of compounds such as dexamethasone which easily crosses the blood brain barrier because of its lipid solubility. Disadvantages are manifold, such as gastrointestinal bleeding, electrolyte disturbances, hyperglycemia, reduction of immunocompetence, increased metabolic needs, and mental disturbances. (3) Nonsteroidal anti-inflammatory drugs that reduce local capillary leakage, such as indomethacin, probenecid and ibuprofen which cross the blood brain barrier. A disadvantage is that the pharmacological effect is not certain. (4) Anti-hypertension drugs that reduce the capillary leakage by lowering filtration pressure, by means of, e.g., nitroprusside. Disadvantages are the reduction of cerebral perfusion pressure and the changes for the worse for brain inflammation due to the increased capillary permeability of the blood brain barrier. However, none of these treatments improves brain inflammation.
To add to the difficulties faced by the clinician in treating brain inflammation, this condition does not present a unitary symptomatology. The inflammatory response in the brain occurs in three distinct phases, each apparently mediated by different mechanisms. First, there is an acute transient phase characterized by local vasodilation and increased capillary permeability. This is followed by a delayed, subacute phase, most prominently characterized by infiltration of leukocytes and phagocytic cells. Finally, a chronic proliferative phase sets in, in which necrosis of brain cells occurs, and glia cells appear where subsequently, however, its original function is lost.
Brain inflammation can be assessed by various techniques such as histochemistry and electron microscopy. However, the most significant parameter to quantify is probably the development of brain edema. Therefore, another approach has been to measure the amount of edema developed in injured tissue. Edema results from the influx of water caused by inflammation and is observed clinically as swelling. This can be quantified by comparing tissue before and after desiccation. The dry weight remaining after drying enables calculation of the amount of fluid evaporated. The fluid evaporated is the amount of edema that was formed.
Another common laboratory technique is to determine the influx of a water-soluble dye such as Evans blue albumin into the central nervous system. By coupling this to a fluorescent technique, the distribution of edema can be measured. More sophisticated and expensive methods such as PET (Positron Emission Topography), CT, MRI (Magnetic Resonance Imaging) as well as radioscintigraphy have been used as well.
However, the above methods can assess only the edema that is formed by the increased permeability of the blood-brain barrier, but they cannot assess the infiltration of leukocytes and phagocytic cells into the central nervous system. Overall, edema plays a very serious role in the pathology of brain inflammation by increasing the intracranial pressure, leading to damage of the brain tissue. Additionally, the increased permeability of blood vessels brings about brain edema, and then, infiltration of white blood cells (WBC) is induced, resulting in a more serious pathological condition, since lysosomal enzymes such as collagenase and esterase damage brain tissue directly. Therefore, determination of the changes in permeability of the blood brain barrier by means of measuring the cerebrospinal fluid (CSF) volume and the WBC count in CSF is essential.
As mentioned above, it has long been believed that in order to be effective in the brain, a drug must be able to cross the blood-brain barrier. Conventional targeting strategies have sought to circumvent this barrier either directly or indirectly, by administering prodrugs whose metabolites do cross the barrier or by attempting to disrupt the integrity of the blood-brain barrier in some way. See, e.g., Pardridge, (2002). To date, however, such a clinically effective agent has never been reported (Wilkinson et al., 2001).
There is therefore a need for a treatment that can be used on both an acute and a semi-acute basis to treat and inhibit the development of brain inflammation. The ideal compound or compounds would have minimal side effects including minimal invasiveness into the brain tissue. Additionally a method for monitoring the changes in WBC infiltration into the cerebrospinal fluid in animal models of brain inflammation would also be desirable.
Despite advances in supportive care and medical technology, the mortality rate from sepsis remains high. Sepsis is the most common cause of death in non-cardiac intensive care units, and its incidence appears to be rising. Over the last two decades, the prevailing belief has been that much of the morbidity and mortality of sepsis is attributable to the host's, extreme inflammatory response to bacteria or bacterial products. Indeed, sepsis is defined clinically as the presence of two or more conditions from the group making up what is known as the “Systemic Inflammatory Response Syndrome” (SIRS), manifested in response to a variety of severe clinical insults, these conditions being: a body temperature higher than 38° C. or lower than 36° C.; a heart rate greater than 90 beats per minute (bpm); a respiratory rate greater than 20 breaths/min. or PaCO2 less than 32 torr (4.3 kPa); a white blood cell count of greater than 12,000 cells/mm3 (leukocytosis), or less than 4,000 cells/mm3 (leukopenia), or 10% of the total cell count being immature neutrophils or band neutrophils. This information is summarized in Table 1.
TABLE 1Infection: Microbial phenomenon characterized by an inflammatory response to thepresence of microorganisms or the invasion of normally sterile host tissue by thoseorganisms.Bacteremia: The presence of viable bacteria in the blood.Sepsis: The systemic response to infection or trauma. This systemic response ismanifested by two or more of (SIRS) conditions as a result of infection.Severe sepsis: Sepsis associated with organ dysfunction, hypoperfusion or hypotension.Hypoperfusion and perfusion abnormalities may include, but are not limited to lacticacidosis, oliguria or acute alteration of mental status.Septic Shock: Sepsis with hypotension, despite adequate fluid resuscitation, along withthe presence of perfusion abnormalities that may include, but are not limited to lacticacidosis, oliguria or acute alteration of mental status. Patients who are on inotropic orvasopressive agents may not be hypotensive at the time that perfusion abnormalities aremeasured.Sepsis induced hypotension: A systolic BP of <90 mm Hg or of >40 mm Hg frombaseline in the absence of other causes for hypotension.Multiple Organ Dysfunction Syndrome: Presence of altered organ function in anacutely ill patient such that homeostasis cannot be maintained without invention.
In pre-clinical animal studies, agents designed to limit this inflammatory response observed in sepsis have shown some initial promising effects. However, this initial promise has not been borne out in subsequent clinical investigations. Two main approaches have been taken: (1) Use of anti-inflammatory therapies; and (2) Use of anti-endotoxin therapies.
With respect to the use of anti-inflammatory therapies, at least three different types of agents have been found to directly limit the production or biologic effects of pro-inflammatory mediators. The agents of interest are: (1) steroids such as glucocorticoids; (2) antagonists or blockers of such pro-inflammatory cytokines as TNF-α and Interleukin-1β; and (3) antagonists or blockers of products generated during inflammation, such as bradykinin, or inflammatory mediators such as prostaglandin and platelet-activating factor (PAF).
With respect to steroids, such as glucocorticoids, a large dose of hydrocortisone has been shown to exacerbate an inflammatory response or to have no effect, but a smaller dose appears to have a beneficial effect even though it is not a sufficiently effective remedy for sepsis.
With regard to the blocking of specific cytokines, such as TNF-α and Interleukin-1β, it has been observed that despite promising results from animal studies, monoclonal antibodies to TNF-α or soluble TNF-α receptors have been shown to have no effect in clinical trials. Further, interleukin-1β receptor antagonists appear to have no beneficial effect in clinical trials.
Finally, it also appears that other mediator specific-inflammatory therapies including platelet-activating factor (PAF), bradykinin and prostaglandin, and the use of antagonists thereto were found to have no effect in clinical trials.
The second strategy targets bacterial products in the circulation with the expectation that neutralizing these bacterial toxins will limit the host pro-inflammatory response and thereby improve outcome. Substances employed include antisera, polyclonal antibodies and monoclonal antibodies.
Because pre-clinical animal studies limited the host pro-inflammatory response using both strategies, clinical trials for sepsis treatment were attempted. However, the clinical trials did not prove successful except for low dose steroid treatment. These findings are summarized in Table 2.
TABLE 2MedicineEffect1. Anti-Inflammatory TherapyGlucocorticoidsHydrocortisonelarge dose (100 mg i.v. then 0.18/kg/hr)none or worsesmall dose (100 mg i.v./every 8 hours)effectiveMediator Specific Anti-Inflammatory TherapyAnti-TNF-αMonoclonal antibody to TNF-αnoneSoluble TNF-α receptor antagonistnone or worseAnti-Interleukin-1Interleukin-1 receptor antagonistsnoneOther Mediator Specific Anti-Inflammatory TherapyAnti-PAFPAF Receptor AntagonistnoneAnti-BradykininBradykinin AntagonistnoneAnti-ProstaglandinCyclooxygenase Inhibitornone2. Anti-Endotoxin TherapyAntiserumnonePolyclonal AntibodynoneMonoclonal Antibodynone
Furthermore, the mortality rate from sepsis is high (35–50%), in spite of this steroid treatment. It has been an important clinical priority to find an effective sepsis therapy.
The reasons for these findings might be a failure to monitor how anti-inflammatory agents act on each step of inflammation in the pre-clinical studies.
There is a major medical need for a treatment that can be used not only for treatment of chronic brain inflammation, but also on an acute and subacute basis, to treat, prevent or inhibit the development of brain inflammation. Furthermore, there is a major medical need for a treatment that can be used not only for treatment of chronic sepsis, but also on an acute and subacute basis, to treat, prevent or inhibit the development of sepsis. These are very serious, important, and unmet medical needs. The ideal compound or compounds would have minimal side effects.
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